Yikes....... what happened?
Unfortunately, one of the big weaknesses of the Internet standards for email is that a sender's address is not verified and does not have to be genuine. Therefore, they are easily forged. Have you ever received email from yourself that you didn't send? That's an example of sender forgery.
It goes on all day, every day, and this particular instance probably has nothing to do with sksboards. There are hacker utilities out there that scan the web for forum software like phpBB, vBulletin and SMF (this site's forum software). The utilities will try to harvest email addresses from sites running the software, and then construct and send bogus emails in an attempt to infect individual PCs with malware of some type.